Treatment for childhood cancer interferes with normal bone maturation such that maximal peak bone mass may never be attained by some survivors of childhood cancer. In childhood cancer survivors, a randomized trial evaluating the effectiveness of vitamin D and calcium supplementation among ALL survivors is currently underway; however, few other interventions have been offered for this at risk population. Recent evidence demonstrates that low magnitude; high frequency mechanical stimulation can improve bone quantity and quality, perhaps providing an alternative or adjunct to pharmacologic intervention in populations where additional medications are either contraindicated or not acceptable to the individuals at risk. This application proposes a prospective double blind randomized clinical trial of low magnitude, high frequency mechanical (LMHF) stimulation for childhood cancer survivors whose bone mineral density is one or more standard deviations below the mean for their age and gender.